Process for the production of polyisocyanates with a biuret structure

ABSTRACT

Comparatively low viscosity biuret containing polyisocyanates are produced by reacting diisocyanates and biuretizing agents in proportions corresponding to a molar ratio of diisocyanate to monofunctional biuretizing agent of at least 11 : 1.



1. A PROCESS FOR PRODUCING A POLYISOCYANATE WITH A BIURET STRUCTURE SAIDPOLYISOCYANATE HAVING A MAXIMUM VISCOSITY OF 50,000 CP AT 20*C SAIDPROCESS COMPRISING A. REACTING (1) EXCESS QUANTITES OF AN ORGANICDIISOCYANATE HAVING ALIPHATICALLY BOUND ISOCYANATE GROUP WITH (2) ABIURETIZING AGENT SELECTED FROM THE GROUP CONSISTING OF WATER ANDORGANIC COMPOUNDS WHICH CONVERT ORGANIC ISOCYANATES INTO THECORRESPONDING BIURETS AT ELEVATED TEMPERATURES THE SUBSTITUTEENTS OFSAID ORGANIC COMPOUNDS BEING INERT IN THE BIURETIZATION PROCESS AND NOTFORMING A CONSTITUENT OF THE BIURET AT A TEMPERATURE OF FROM 60* TO250*C AND B. REMOVING EXCESS UNREACTED DIISOCYANATE SAID PROCESSCHARACTERIZED IN THAT THE ORGANIC DIISOCYANATE AND BIURETIZING AGENT AREUSED IN PROPORTIONS CORRESPONDING TO A MLAR RATIO OF DIISOCYANATE TOMONOFUNCTIONAL BIURETIZING AGENT OF AT LEAST 11:1.
 2. A process for theproduction of a polyisocyanate with a biuret structure which has amaximum viscosity of 4000 cP at 20*C in accordance with claim 1,characterized in that the organic diisocyanate used is hexamethylenediisocyanate.
 3. A process according to claim 1 characterized in thatthe biuretizing agent used for the biuretizing reaction comprises formicacid and the reaction temperature is kept at 60* to 120*C; wherebyN-formylated urea diisocyanates, which substantially reduce theviscosity, are obtained in addition to the biuret polyisocyanate.
 4. Aprocess according to claim 1 characterized in that the biuretizing agentused is a tertiary monoalcohol.
 5. A process according to claim 4characterized in that the tertiary alcohol used is tert.-butanol.